Personal reflections

Background

To evaluate the performance of hydrogen infrastructure for fuel cell vehicles, the Commonwealth of Pennsylvania is considering granting an operating permit to a commercial network or methanol reforming hydrogen fuel stations just outside of Pittsburgh, Harrisburg, and Philadelphia.

Hydrogen is a pollution-free method of energy storage and transfer, however it is not very dense making transportation costs prohibitive, and can be explosive in less than ideal conditions. The new prototype hydrogen fuel stations will attempt to solve this problem by transporting hydrogen around the state from the energy production facilities to the fueling stations in the form of methanol (CH3OH), which is a liquid under most normal conditions. At the fueling stations the methanol will be converted to hydrogen gas for use in personal and commercial fleet vehicles.

Methanol resolves many of the transportation efficiency and safety issues associated with transporting gaseous hydrogen, but it necessitates that each fuel station process or reform the methanol rather than just store it as existing fuel stations treat gasoline and diesel.

Initially, 10 fuel stations would be constructed, but if the project proves successful, several hundred of these methanol reforming hydrogen fuel stations may be constructed across the state. State regulators charged with issuing the permit and conducting oversight want to be aware of all potential problems with this technology as well as the main risks to its long term success in the market as a competitor to traditional fuels. These risks include the inevitable backlash against the technology if it proves responsible for any worker or public deaths or serious injuries.

In order to transform the methanol into hydrogen, a process known as catalytic steam reforming will be used. In this process, water is mixed with the methanol on a 1:1 basis (by molar weight), heated and converted to vapor in the presence of a catalyst producing a mixture of hydrogen gas and carbon dioxide. A compression and cooling of this mixture allows the carbon dioxide to be separated from the hydrogen, which can be stored until needed.

Basic Assumptions

You may assume that utilities including potable water supply, electricity, and natural gas are provided with 100% reliability.

Design Information

The methanol steam reformer system hardware schematic is shown in Figure 3 below:

 

Figure 3: Design of the methanol steam reforming system to be installed at each hydrogen fuel station. 

Liquid water and natural gas is provided by municipal supplies. The methanol (CH3OH) is carried by trucks that arrive regularly to maintain fuel supplies. These two supplies are combined on a 1:1 molar ratio and transferred to a gas-fired heater, which boils the combined fluid and converts it to a vapor at 300°C. The metal oxide catalyst in the reactor aids conversion of the methanol-steam mixture to a mixture of carbon dioxide gas and hydrogen gas. This gas is compressed and cooled, allowing the carbon dioxide to be separated as a liquid and stored for later disposal, while the hydrogen gas is transferred to a pressurized storage tank at 3000 psi, from which it is dispersed to vehicles on demand.

The methanol steam-reforming reaction is as shown in the following relation:

CH3OH + H2O   ⟶⟶    CO2 + 3H2

Component	Replacement Costs	Replacement Time	Recommended Maintenance	Characteristic Life (hours)	Weibull Shape Factor (beta)	Failure Rate Penalty for Skipping PM [# of failures per year]
Fired Heater	$50,000	8 hours	Refurbish (every 2 years) [4 hours] Inspect (every month) [2 hours]	100,000	1.1	0.095 * yr
Catalytic Reactor 1	$100,000	12 hours	Replace Catalyst (each year) [4 hours] Inspect Reactor (every week) [2 hours]	800,000	1.7	0.0003
Catalytic Reactor 2	$100,000	12 hours	Replace Catalyst (each year) [4 hours] Inspect Reactor (every week) [2 hours]	800,000	1.7	0.0003
Gas Separator	$15,000	2 hours	Refurbish (every year) [3 hours] Inspect (every week) [2 hours]	500,000	3.8	0.075 * yr
Cooler	$60,000	6 hours	Reburbish (every year) [4 hours] Inspect (every month) [1 hour] Test (every week) [2 hours]	250,000	2.2	0.0004
Fluid Mixer	$10,000	4 hours	Refurbish (every 9 months) [2 hours] Test (every month) [1 hours]	600,000	3.1	0.00025 * yr
Hydrogen Storage Tank	$50,000	20 hours	Inspect Tank (every week) [1 hour] Test (every month) [2 hours]	200,000	0.9	0.000015
Methanol Storage Tank	$25,000	6 hours	Inspect Tank (every week) [1 hour]	100,000	0.8	0.0001
Water Storage Tank	$25,000	6 hours	Inspect Tank (every week) [1 hour]	100,000	1.3	0.0001
Compressor	Data available in April.
Reverse Osmosis Filter	Data available in April.

It can be assumed that utilities including potable water supply, electricity, natural gas are provided with 100% reliability.

Maintenance Details

There is a scheduled down period of 4 hours every night when the fuel station will be closed. This time can be used for preventive and corrective (reactive) maintenance activities without affecting productivity of the station. There will be only one maintenance team available, so if more than 4 hours of maintenance are required on a given day, then operational time would be lost. 

There are two catalytic reactors. When one is failed, the system can continue to operate at 50% typical throughput. All other failures result in a shut down until the failure can be repaired.

There is a maintenance company on contract trained in repairing these kinds of facilities. Their hourly rate is $150 per hour. 

Maintenance activities for each component should be considered as "all or nothing" decisions. If all of the maintenance is completed for that component, then the failure rate penalty is avoided. If no maintenance is performed on that component, then the failure rate penalty is accepted. 

Table 1: Methanol Reformer Component Reliability and Maintenance Requirements

Economic Benefits

The hourly profit of the fuel station (income minus the cost of inputs and utilities) is anticipated to be $250 per hour. The station will operate normally for 20 hours per day, 365 days per year. If you recommend additional maintenance than can be accomplished within the 4-hour scheduled downtime period each day, then those hours could be reduced. 

Disasters

While the probability of any safety or environmental problem should be derived from your team’s FMECA, the distribution of the severity of such events should follow a Poisson distribution with a mean of 2.5 out of a 5-level severity scale. This means that any particular safety- or environmental-related failure mode will result in an event of an uncertain severity as determined by this distribution.

Detection and Warning Equipment

A variety of detection and warning systems are available for incorporation into the fuel station design. Some of their detection abilities and prices are included in the table below.

Table 2: Detector Performance Specifications

Type of Detector	Price	Positive Detection Rate P(Detect|Presence)	Non-Detection Rate P(No Detect|No Presence)
Hydrogen	Data available in April.
Methanol Vapor
Methane

 

Likelihood and Severity Scales

Table 3: Severity Scale

Catastrophic	A fatality or a permanent total disabling industry. A financial loss of more than $500,000.
Critical	A permanent, partially disabling injury or a moderate injury to 10 or more people. A financial loss of more than $150,000, but less than $500,000.
Moderate	A temporarily disabling injury or a marginal injury to more than 10 people. A financial loss of more than $50,000, but less than $150,000.
Marginal	A minor, temporary injury. A financial loss of more than $1,000, but less than $50,000.
Negligible	An injury requiring no more than first aid and no lost worktime. A financial loss of less than $1,000.

Table 4: Likelihood Scale

Frequent	P = 1 in 10. Occurs multiple times a year.
Probable	P = 1 in 100. More likely to occur during a year than not.
Improbable	P = 1 in 1,000. May happen during a year.
Remote	P = 1 in 10,000. Not likely to occur in a year.
Rare	P = 1 in 100,000 or less.

Supplemental Information

The following reports and information may aid your analysis of the risks of the system.

· Chemical Safety Report (available: TBD)

· Environmental Impact Report (available: TBD)